The present invention relates to a process for the extrusion of melt processable liquid crystal polymer. The process provides for improved processability of the liquid crystal polymer and yields shaped articles having improved properties.
Melt processable liquid crystal polymers are well-known in the art. These polymers commonly exhibit very high melting temperatures and hence must be processed at inconveniently high temperatures. Moreover, prolonged exposure to high temperatures commonly causes degradation of the polymer and results in the production of shaped articles having relatively poor properties.
It has now been found that melt processable liquid crystal polymers can be processed at decreased temperatures by controlling the thermal history of the polymer. Specifically, it has been found that shaped articles having improved mechanical properties can be formed from liquid crystal polymer which has been subjected to an elevated temperature between the DSC transition temperature and the degradation temperature of the polymer, cooling the liquid crystal polymer to a processing temperature which is between the DSC transition temperature and the elevated temperature, and extruding the liquid crystal polymer into the form of a shaped article. Preferably, a substantial decrease in melt viscosity occurs when the liquid crystal polymer is subjected to the elevated temperature and, upon cooling, the liquid crystal polymer substantially retains the lower melt viscosity exhibited by the liquid crystal polymer at the elevated temperature. The reduction in melt viscosity is retained for a period of time sufficient to allow melt processing of the liquid crystal polymer at lower temperatures. As a result, the liquid crystal polymer may be processed at a lower temperature between the DSC transition temperature and the elevated temperature, the combination of the relatively low processing temperature and the reduction in melt viscosity providing an improvement in processability of the liquid crystal polymer.
The process of the present invention is especially applicable to liquid crystal polymers having relatively high DSC transition temperatures. By employing the process of the present invention, such polymers can be conveniently processed at temperatures near the DSC transition temperature rather than at the higher temperatures commonly encountered in the prior art at which degradation is more likely to occur. This improved processability is believed to be due to the liquid crystal polymer substantially retaining, upon being cooled to the processing temperature, a reduction in melt viscosity which may be achieved by subjecting the liquid crystal polymer to the elevated temperature. The liquid crystal polymer melt can therefore be extruded at a lower, more convenient processing temperature while the melt retains a reduction in melt viscosity which has heretofore been thought to be available only at increased temperatures. Hence, the process of the present invention provides for the melt processing of liquid crystal polymer while taking advantage of a combination of relatively low processing temperature and a reduction in melt viscosity. Moreover, the shaped articles produced according to the present invention exhibit improved mechanical properties as a result of the improved processing conditions employed herein.
Therefore, it is an object of the present invention to provide an improved process for the extrusion of melt processable liquid crystal polymer.
It is also an object of the present invention to provide a process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics and which yields shaped articles having improved properties.
It is also an object of the present invention to provide a process for the extrusion of melt processable liquid crystal polymer, wherein the thermal history of the liquid crystal polymer is controlled, thereby providing improved processability characteristics and yielding shaped articles having improved properties.
It is also an object of the present invention to provide a process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics and which yields shaped articles having improved properties, wherein the liquid crystal polymer can be conveniently processed at a relatively low temperature at which polymer degradation is minimized due to control of the thermal history of the polymer.
It is also an object of the present invention to provide a process for the extrusion of melt processable liquid crystal polymer which provides improved processability characteristics and which yields shaped articles having improved properties, wherein the liquid crystal polymer can be conveniently processed at a relatively low processing temperature due to a significant reduction in the melt viscosity of the polymer which is "remembered" by the polymer at the lower temperature and which is achieved by controlling the thermal history of the polymer.
These and other objects as well as the scope, nature, and utilization of the present invention will be apparent from the following description and appended claims.